The invention relates to a device for dispensing a fluid, in particular a fluid such as beer or the like, from a storage space of a container via at least one closeable dispenser outlet to the outside, comprising a pressure reservoir which is separated from the storage chamber and in which a pressurized propellant is accommodated, and which can be connected to the storage chamber via a pressure regulation mechanism.
Such a device is known from U.S. Pat. No. 5,368,207.
This latter device is a pressurized container, for example a spray can, comprising a first chamber in which a liquid under gas pressure is accommodated and can be dispensed from the container via a valve of the kind commonly found in spray cans. In order to produce the pressure in the first chamber of the container, a second chamber is provided inside the container, in which the second chamber a propellant is accommodated under high pressure. The propellant can be discharged from the second chamber into the first chamber via a pressure regulator provided to ensure that a constant pressure is maintained inside the first chamber. The pressure regulator includes a plunger that can be moveably guided inside a closed housing and is sealed at both ends against the housing wall. In combination with the housing, the plunger encloses at its one end a third chamber that is pressurized to a predetermined reference pressure. At the opposite end of the plunger, a lateral through opening to an outlet is formed that communicates with the first chamber and which can be opened or closed depending on the axial position of the plunger. Between each of the two ends of the plunger and the housing, a cavity is also enclosed due to a reduction in the diameter of the plunger, the cavity being connected via an inlet opening to the second chamber, in which the pressurized propellant is accommodated. Depending on the position of the plunger, propellant is thus able to escape from the second chamber into the first chamber of the container. If, for example, the pressure in the first chamber of the container decreases, for example because fluid is dispensed to the outside via the valve, this will lead to a displacement of the plunger in the direction of the open position due to the reference pressure in the third chamber acting upon the plunger. Hence, propellant is discharged from the second chamber into the first chamber, which leads to a pressure increase in the first chamber. The pressure regulator tries in this way to establish an equilibrium pressure in the first chamber that substantially depends on the reference pressure inside the third chamber.
Although such a pressure regulation mechanism is basically suitable for generating an approximately constant pressure inside a container, such as inside a spray can, the pressure regulation concept being applied involves considerable disadvantages.
If such a container is used, for example, to dispense carbonated beverages, such as beer, as known from DE 298 22 430 U1, for example, it is desirable to maintain a constant pressure that preferably corresponds to the equilibrium pressure between the fluid and the gas, regardless of the ambient pressure around the container. If one considers, for example, the specific application in party kegs with a volume of three, five or ten liters, for example, and in which beer is stored under CO2 pressure, the pressure to be maintained even when drafting the beer, the resultant equilibrium pressure between the beer and the CO2 is a function of the solubility of CO2 in beer. Depending on the temperature, the absolute pressure is in the order of approximately 0.5 to 2 bar at temperatures between about 5° C. and 10° C. This means that an overpressure of about 0.5 to 1 bar relative to the ambient pressure should be maintained in the container. However, maintaining the reference pressure inside the third chamber is difficult over a longer period. Especially when manufacturing tolerances are taken into consideration, a certain loss of pressure from the reference chamber can be expected for storage periods lasting several months, which naturally leads to a corresponding drop in the pressure over the liquid as adjusted by the pressure regulator. Even when using high-quality precision-made parts with small tolerances, losses due to diffusion and migration can be expected in the course of time because it is difficult to achieve a perfect seal of a gas volume over a longer period of time. There is therefore a risk, especially after a long period in storage, that the reference pressure will drop over time, with the result that the pressure regulator is no longer able to set the desired pressure over the liquid.